Magnetic and MO media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in, e.g., disk form, such as utilized in computer-related applications, comprises a non-magnetic, disk-shaped substrate, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (Al)-based alloy, such as aluminum-magnesium (Al—Mg), having at least one major surface on which a layer stack or laminate comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers may include, in sequence from the substrate deposition surface, a plating layer, e.g., of amorphous nickel-phosphorus (Ni—P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy, such as chromium-vanadium (Cr—V), a magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of a carbon (C)-based material, e.g., diamond-like carbon (“DLC”) having good tribological properties. A similar situation exists with MO media, wherein a layer stack or laminate is formed on a substrate deposition surface, which layer stack or laminate typically comprises a reflective layer, e.g., of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE-TM) alloy layers, one or more transparent dielectric layers, and a protective overcoat layer, e.g., a DLC layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
In operation of such disk-shaped magnetic and/or MO media, a typical contact start/stop (CSS) method commences when a data transducing head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk, where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk, and stopping.
For optimum consistency and predictability, it is necessary to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. Accordingly, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to excessive stiction and friction during the start up and stopping phases, thereby causing wear to the head and recording surfaces, eventually leading to what is referred to as a “head crash.” Thus, there are competing goals of reduced head/disk friction and minimum transducer flying height.
According to conventional practices, a lubricant topcoat is uniformly applied over the protective overcoat layer to prevent wear between the disk and the facing surface of the read/write transducer head during CSS operation because excessive wear of the protective overcoat layer increases friction between the transducer head and the disk, eventually leading to catastrophic failure of the disk drive. However, an excess amount of lubricant at the head-disk interface causes high stiction between the head and the disk, which stiction, if excessive, prevents starting of disk rotation, hence causing catastrophic failure of the disk drive. Accordingly, the lubricant thickness must be optimized for stiction and friction.
The continuing requirements for increased recording density and faster data transfer rates necessitating lower flying heights of the data transducing heads and minimized friction/stiction of the head-disk interface have served as an impetus for the development of specialized lubricants for serving as the lubricant topcoat layer overlying the protective overcoat layer. Such lubricants are required to fulfill a variety of functions requiring diverse characteristics and attributes. For example, the lubricant material forming the topcoat layer must be chemically inert, have a low vapor pressure, low surface tension, high thermal stability, mechanical stability under shear stress, and good boundary lubrication properties. In addition to the foregoing, it is critical that the lubricant adhere tightly (as, for example, reflected in the “bonded lube thickness” or “bonded lube ratio”) to the underlying surface, i.e., the protective overcoat layer (typically carbon-based), over the lifetime of the disk drive comprising the recording disk and associated flying head data transducer.
Fluoropolyether lubricants have been developed which are in widespread use as materials for forming the lubricant topcoat layers of disk-shaped data/information storage and retrieval media, e.g., magnetic and MO recording media. Fluoropolyether-based lubricants are uniquely suited for use as lubricant topcoat layers in such rotating disk-type recording media in view of their exemplary properties, including inter alia, chemical inertness, low vapor pressure, low surface tension, high thermal stability, mechanical stability under high shear stress, and good boundary lubrication properties. Among the many currently available fluoropolyether lubricants, liquid perfluoropolyethers (PFPE) and derivatives thereof are most commonly employed in forming lubricant topcoat layers on rotatable recording media.
Commercially available PFPE lubricants include KRYTOX™ (DuPont Co., Wilmington, Del.); FOMBLIN™ Z-DOL, Z-TETRAOL, Z-DOL TXS, AM 2001, and AM 3001 (Ausimont Montedison Group, Thorofare, N.J.); and DEMNUM™ SA, SH, SP, and SY (Daikin Industries, Ltd., Osaka, Japan). A number of these commercially available PFPE-based lubricants are substituted with 2 to 4 polar end-groups, such as 2-4 hydroxyl or carboxyl groups, which polar end-groups are provided for enhancing adhesion of the polymeric lubricant molecules to the surface of the recording media, e.g., the surface of a carbon-based protective overcoat layer. Application of the PFPE-based lubricants to the media surface may be performed by any standard technique, e.g., dipping, spraying, spin coating, etc., followed by drying to remove any volatile solvent(s) therefrom, and if desired, followed by tape burnishing. A more recently developed technique for applying thin films of polymeric lubricants to media surfaces comprises generation of a vapor of the lubricant followed by condensation of the vapor on the media surface.
As indicated above, conventional PFPE-based lubricants generally comprise 2-4 polar groups or moieties at either end of a generally linear, perfluorinated alkylpolyether molecule, for facilitating direct bonding to a surface, and thus provide improved adhesion of the lubricant topcoat layer to the surface of the protective overcoat layer. Such polar functional groups, however, are not necessarily chemically inert, i.e., they may exhibit varying degrees of chemical inertness, and consequently, the above-described conventional PFPE-based lubricants may disadvantageously undergo chemical reactions prior or subsequent to their application to the media surface. In particular, contamination of the lubricant topcoat layer with a Lewis acid, e.g., aluminum oxide (Al2O3), may promote rapid degradation of the lubricant topcoat layer. Furthermore, as the thickness of each of the carbon-based protective overcoat and lubricant topcoat layers are continuously being reduced in view of the ever-increasing requirements for recording media with ultra-high areal storage density, advanced lubricants which provide improved mechanical protection as well as improved lubricity are required.
In view of the above, there exists a clear need for improved methodology for applying or forming thin films of advanced polymeric lubricants onto surfaces of thin film recording media, e.g., in disk form, wherein the polymeric lubricant films exhibit improved chemical resistance and tribological properties vis-a-vis the conventional methodology described above. According to the present invention, such goals are met by in situ thermally- or infrared-catalyzed conversion (i.e., polymerization) of suitable precursor lubricant compounds or derivatives into networked (i.e., cross-linked) polymers which are strongly bonded to the surfaces of the protective overcoat layers of the media, wherein the precursor lubricant compounds are derived from conventional lubricant materials, e.g., generally linear perfluoropolyethers or derivatives thereof.
The present invention thus addresses and solves problems and difficulties in achieving high performance lubricant thin films for use in the manufacture of thin film, disk-shaped magnetic and MO data/information storage and retrieval media, while maintaining full compatibility with all aspects of conventional automated manufacturing technology therefor, including productivity requirements necessary for economic competitiveness. In addition, the present invention provides improved thin film magnetic and MO media having stabilized, chemically networked or cross-linked lubricant films derived from a precursor lubricant material. Further, the methodology afforded by the present invention enjoys diverse utility in the manufacture of various other devices and/or articles requiring formation of stable, high performance lubricant thin films thereon.